With radios it's all about the features and the capabilities.
You want an FM 75mhz radio because it's less glitchy than the AM radios and you have more frequency choices in the 75mhz band (this comes in handy when you have a bunch of RC's together).
Next, you need things like end point adjustments and exponential settings.
If at all possible, you should find a good radio that has a lot of nice features and then just tuck you money away in the piggy bank until you have enough to buy it. In the end, you'll be glad that you held out for what you wanted.
NA what radio do you have? It's like an Airtronics or something? That one sounds like a nice radio for the price. Maybe he can fill you in. He also races on-road so maybe there are some features we off-road folks don't care about.
Good Luck,
Rob